A negative-retarder (a phase-difference element having a negative phase-difference in the vertical direction to the element plane) is known as a phase-difference plate which gives optical compensation to the characteristics of angle of visibility (angle-dependency of phase-difference) on a vertically aligned (VA) type liquid crystal display by inserting the phase-difference plate between a liquid crystal cell and a polarization element, both of which are the components of a liquid crystal display unit.
That type of negative-retarder is prepared by a procedure given below. First, a resin film is subjected to uniaxial stretch while allowing free shrinkage thereof in the direction perpendicular to the stretching direction to form a stretched film that satisfies the condition of Nx>Ny≧Nz, (Nx is the intraplane refractive index in the stretching direction, Ny is the intraplane refractive index in the direction perpendicular to the stretching direction, and Nz is the refractive index in the thickness direction). Secondly, the stretched film is cut to prepare a rectangular chip in which the longer side thereof is along the stretched direction, and another chip having the same shape in which the shorter side thereof is along the stretched direction. Thirdly, those two chips are stuck together using an adhesive or a bond, (what is called the “patching”), so that the respective stretched directions thereof perpendicularly cross each other, thus obtaining the negative-retarder. To manufacture the negative-retarder having the above-described structure, however, there is a problem of repeated troublesome works including sticking the cut-to-form chips together, which degrades the production efficiency.
There is a known phase-difference plate, which is prepared by sticking a stretched film giving a ¼ wavelength phase-difference to a specific wavelength, (¼ wavelength plate), and a stretched film giving a ½ wavelength phase-difference to a specific wavelength, (½ wavelength plate), with each other so that the respective delayed-phase axes thereof cross with each other at a specified angle (for example, 50 to 70 degrees). The phase-difference plate functions as a broad-band ¼ wavelength plate which gives small variations in the phase-difference under wavelength variations. Thus, by laminating with a linear polarization element, the phase-difference plate provides a broad-band circular polarization element which can obtain circular polarization over a wide wavelength range.
The broad-band ¼ wavelength plate is manufactured by cutting or punching each of the stretched films prepared by uniaxial stretching, (a ¼ wavelength plate and a ½ wavelength plate), indifferent directions to the stretched direction, respectively, thus to form chips having the same shape (rectangular shape), and then by sticking them together using an adhesive or a bond.
To manufacture the above-described phase-difference plate (broad-band ¼ wavelength plate), however, there is a problem of repeated troublesome works including cutting (punching) films to form chips, then sticking the chips together, which degrades the production efficiency. In addition, since the cutting is done at a specific angle to the stretched direction, cut-loss is unavoidably generated, which raises a problem of loss in raw material.
The present invention was derived to cope with the above-described situation. A first purpose of the present invention is to provide a long optical laminate which has wanted optical characteristics, has high stability in optical characteristics, is preferably used as a negative-retarder, and gives high production efficiency.
A second purpose of the present invention is to provide a long broad-band ¼ wavelength plate which has high optical compensation performance to the characteristics of angle of visibility, applies the long optical laminate, effectively uses a stretched film as the raw material, and gives high production efficiency.
A third purpose of the present invention is to provide a long optical element and a broad-band circular polarization element which have high performance to provide ¼ wavelength phase-difference to a wide wavelength range, uses the long broad-band ¼ wavelength plate, and gives high production efficiency.
A fourth purpose of the present invention is to provide an optical element having the broad-band circular polarization element, a reflection liquid crystal display unit, a touch panel, and an electro-luminescence display unit.